Clearing in reversal diazosulfonate photoreproduction

ABSTRACT

Inclusion of an alkali metal iodide, fluoroborate, fluorophosphate, or thiocyanate in a reversal diazosulfonate photoimaging formulation improves clearing.

United States Patent South Hadley, Mass.

CLEARING IN REVERSAL DIAZOSULFONATE PHOTOREPRODUCTION 6 Claims, No Drawings U.S. Cl 96/91 R, 96/49 Int. Cl .Q. G03c 1/56, (103:: 1/60 Field of Search 96/49, 75, 91

Primary Examiner- Norman G. Torchin Assistant Examiner-Charles L. Bowers, Jr.

Attorneys-Wm. J. Foley, John A. Weygandt, John W. Kane,

Jr., S. T. Hadley, A. J. McNulty and M. L. Faigus ABSTRACT: lnclusion of an alkali metal iodide, fluoroborate, fluorophosphate, or thiocyanate in a reversal diazosulfonate photoimaging formulation improves clearing.

CLEARING IN REVERSAL DIAZOSULFONATE PI-IOTOREPRODUCTION BACKGROUND OF THE INVENTION 1. Field of the Invention The invention described herein was made under a contract with the United states Air force. The present invention relates to photosensitive diazosulfonate formulations and to diazophotographic reproduction materials made therefrom.

2. Description of the Prior Art In US. Pat. No. 3,479,183, granted Nov. 18, 1969, there is disclosed and claimed a negative-working or reversal diazophotographic reproduction (photoreproduction) material comprising a para-aminobenzene diazosulfonate, a coupler (Le. a color former) therefor and a substantially nonvolatile amine, which material is applied as a discrete layer upon the surface of a support. The image-producing process described in the aforementioned patent comprises the steps of exposing thediazoimaging material to actinic illumination to convert the diazosulfonate to an active diazonium compound which couples with a coupling component to provide a reverse dye image; acidifying the discrete layer with acid vapor; and lightclearing the unreacted diazosulfonate by exposing it to overall actinic illumination, thereby forming colorless decomposition products of the diazosulfonate to produce a stable, fixed negative dye image against a clear background. The mechanism of the negative-working diazosulfonate process during the lightclearing step may be represented in the following manner:

ArN HSO +H l,ArOI-I+H SO +N T (2) wherein Ar is a para-aminobenzene radical and M is an alkali metal.

Since the aforementioned reversal diazoimaging formulation is cleared by destroying the uncoupled diazo compound with light, the clarity of the background is a direct function of the amount of clearing light-energy. A substantial amount of energy has been required to destroy the residual diazosulfonate in photoreproduction materials comprising the formulation disclosed in the above-mentioned patent. As a result of failure to meet this high requirement, the prints have tended to show a lack of brightness in the cleared areas. Furthermore, a clearing time longer than desirable has been required in order to accomplish the clearing step. As a consequence, the printing speed of the reversal diazosulfonate photoreproduction material has been relatively low.

Accordingly, objects of the present invention are to reduce the amount of light necessary to destroy the residual diazo compound, to increase the clearing speed of reversal diazoimaging materials, and to improve the brightness of the cleared areas in such materials.

SUMMARY OF THE INVENTION In accordance with the present invention, the incorporation of an alkali metal iodide in the reversal diazo formulation reduces the amount of light energy necessary to destroy residual diazosulfonate to half that previously required. Further in accordance with the present invention, the incorporation of an alkali metal iodide, an alkali metal fluoroborate, an alkali metal fluorophosphate, an alkali metal thiocyanate, or a combination thereof, in the reversal'diazo formulation produces much brighter background areas, which result is attributable to the virtually complete elimination of diazonium compounds in the cleared portions.

Without wishing to be bound by theory, applicant believes that the following explanation may account for the effect produced in accordance with the present invention. While the reactions which are believed to be involved are known reactions, it has not heretofore been suspected that these reactions proceed under the conditions found in a commercial diazoprinter-processor. Indeed, the reactions given may not, in fact, represent the mechanism by which the improved results are achieved. But since they seem the likeliest explanation, they are included in order to provide a full disclosure of the invention.

In the presence of actinic radiation, the alkali metal iodide gives off iodine (I which oxidizes the diazosulfonate to a diazonium compound. Thus, the amount of light energy required to destroy the residual diazosulfonate in the background areas is reduced, since the action of the actinic radiation on the diazosulfonate in an acid environment (see reactions 1 and 2) is supplemented by the iodine vapor. [See Saunders, The Aromatic Diazo Compounds and Their Technical Applications (2d ed. 1947) pp. 290-291.]In addition, during the clearing step the alkali metal iodide probably also reacts to form hydrogen iodide (III), which in turn replaces the nitrogen on the benzene ring of the diazonium compound (the Griess replacement), thereby reducing it to a stable, inactive form. Saunders, supra at p. 276.

The alkali metal fluoroborates, alkali metal fluorophosphates and alkali metal thiocyanates can, like iodine, replace the nitrogen on the benzene ring of the diazonium compound to reduce it to a stable and inactive form. Thus, these compounds also serve to increase the brightness of the background area by reacting with the residual diazosulfonate. The reaction for the replacement of the diazo group by fluorine through the thermal decomposition of the diazonium fluoroborates is referred to as the Schiemann reaction. See Saunders, supra at p. 283. The modification of the Schiemann reaction by the use of hexafluorophosphoric acid is described by Rutherford et al., 26 Journal of Organic Chemistry 5,149 Dec. 1961). The replacement of the diazo group by the thiocyano group is disclosed by Saunders supra at p. 323.

Accordingly, the reversal diazosulfonate formulation of the present invention contains an alkali metal iodide, an alkali metal fiuoroborate, an alkali metal fluorophosphate or an alkali metal thiocyanate. Any of the diazosulfonate compositions of the invention, when applied as a discrete layer on a support, provides a diazophotographic reproduction material useful for duplicating images contained in media, such as engineering drawings, microfilm and aerial photographs through the action of light on the diazo composition.

While the amount of the alkali metal iodide employed in the formulation of the present invention has not been found to be especially critical within reasonable limits, e.g. below a concentration of twice the molar concentration of the diazosulfonate, an equimolar concentration is preferred. The same is true concerning the concentration of the alkali metal fluoroborates, alkali metal fluorophosphates and alkali metal thiocyanates.

The principles, features and objects of the invention will be further understood from a consideration of the following specific examples.

DESCRIPTION OFTHE PREFERRED EMBODIMENTS Example I A light-sensitive coating formulation comprising the following components was prepared:

2-hydroxy-3-naphtlioie acid, 2,5 dimethoxy anilide, g .1 1.05 3,3-din1ethoxy-4,4 diacetoacetamido biphenyl (b1s-acetoacet-ortho-anisldide), g. 0.65

4-(N-ethy1, N-benzylamino)-benzene diazosulfonate, sodium salt, g Potassium iodide, g

This solution was bead coated onto a sheet of cellulose diacetate film and dried. The film was then exposed to actinic light under a partially opaque master to give a black image in the unprotected-Le, light-struck-areas. The film was then fixed by acidifying with hot acetic acid vapors and the background areas were cleared by re-exposing the entire film to actinic light. This film required two passes through an Ozamatic (a diazo-type processor manufactured by the Ozalid Division of GAF Corporation) at 1% feet per minute to obtain a clear background. By comparison, a film which did not contain the potassium iodide required three passes at that speed and the background obtained was not as bright.

Example 11 A light-sensitive coating coating formulation comprising the following components was prepared:

This solution was coated by means of a No. 36 Mayer bar, onto a sheet of polyester treated with a suitable bonding layer and dried. The resulting film was then exposed to actinic light under a partially opaque master to give a black image in the unprotected-Le. light-struck-areas. The film was then fixed and the background areas cleared by acidifying with formic acid vapors and re-exposing the entire film to actinic light. This film required six passes through a Tecnifax Hi-R (a diazotype processor manufactured by the Plastic Coating Corporation) at 8 feet per minute to obtain a cleari.e. nonyellow background with a brightness of 61.0 as measured with a photoelectric brightness meter, using white cararra glass as the brightness standard. By comparison, a control without the sodium iodide required 17 passes at the same speed and the brightness obtained had a value of 56.0.

Example 111 A light-sensitive coating formulation comprising the following components was prepared:

This solution was coated, by means of a No. 36 Mayer bar, onto a sheet of ethyl-cellulose-treated, baryta-sized paper and dried. The paper was then exposed to actinic light under a partially opaque master to give a black image in the unprotectedi.e. 1ight-struckareas. The print was then fixed and the background areas cleared by acidifying with formic acid vapors and reexposing the entire sheet to actinic light. Three passes through the Tecnifax Hi-R at 4 feet per minute were required to obtain a clear background. By comparison, a sheet which did not contain the lithium iodide required six passes at the same speed to clear.

Example IV A light-sensitive coating formulation comprising the following components was prepared:

This solution was coated on paper, printed and cleared as in example 111. Three passes through the Tecnifax Hi-R at 4 feet per minute were required to obtain a clear background. By comparison, a sheet which did not contain the sodium iodide required six passes to clear under the same conditions.

Example V A light-sensitive coating formulation comprising the following components was prepared:

Various alkali metal salts were added to this formulation, coated on polyester, and printed to give the following results. Brightness measured with a photoelectric brightness meter, using white cararra glass as the brightness standard.

Background Added salt Brightness None (control) 6L0 l gv Nal 68.5

2 g. Nal 70.0 L25 g. Lil-3H,0 70.0 0.75 g. Lil-3H,0+O.777 g. LiPGF, 71.0 1.11 g. Kl 67.5 0.73 g. NaBF. 69.0 1.23 g. KPF, 70.0 0.65 g. KSCN 66.5

Other commercially available compounds which can be incorporated in the light-sensitive formulation of the invention to increase brightness in the clear areas include lithium fluoroborate, potassium fluoroborate, lithium thiocyanate, and sodium thiocyanate.

While the invention has been described with reference to preferred embodiments thereof, it is understood that various other changesand modifications thereof will occur to a person of ordinary skill in the art without departing from the spirit and scope of the invention, as defined by the appended claims.

What is claimed is:

1. In a reversal diazoimaging coating formulation comprising a para-amino benzene diazosulfonate, an azocoupling component, and a substantially nonvolatile amine, the improvement which comprises the inclusion of an alkali metal iodide, an alkali metal fluoroborate, an alkali metal fluorophosphate, or an alkali metal thiocyanate in said formulation.

2. ln a reversal diazoimaging coating formulation comprising a para-amino benzene diazosulfonate, an azocoupling component, and a substantially nonvolatile amine, the improvement which comprises the inclusion of an alkali metal iodide in said formulation.

3. In a reversal diazoimaging coating formulation comprising a para-amino benzene diazosulfonate, an azocoupling component, and a substantially nonvolatile amine, the improvement which comprises the inclusion of an alkali metal fluoroborate an alkali metal fluorophosphate, or an alkali metal thiocyanate.

4. A reversal diazophotoreproduction material comprising a support and a photosensitive layer coated on a surface of the support, the layer comprising the imaging coating formulation according to claim 1.

5. A reversal diazophotoreproduction material comprising a support and a photosensitive layer coated on a surface of the support, the layer comprising the imaging coating formulation according to claim 2.

6. A reversal diazophotoreproduction material comprising a support and a photosensitive layer coated on a surface of the support, the layer comprising the imaging coating formulation according to claim'3. 

2. In a reversal diazoimaging coating formulation comprising a para-amino benzene diazosulfonate, an azocoupling component, and a substantially nonvolatile amine, the improvement which comprises the inclusion of an alkali metal iodide in said formulation.
 3. In a reversal diazoimaging coating formulation comprising a para-amino benzene diazosulfonate, an azocoupling component, and a substantially nonvolatile amine, the improvement which comprises the inclusion of an alkali metal fluoroborate, an alkali metal fluorophosphate, or an alkali metal thiocyanate.
 4. A reversal diazophotoreproduction material comprising a support and a photosensitive layer coated on a surface of the support, the layer comprising the imaging coating formulation according to claim
 1. 5. A reversal diazophotoreproduction material comprising a support and a photosensitive layer coated on a surface of the support, the layer comprising the imaging coating formulation according to claim
 2. 6. A reversal diazophotoreproduction material comprising a support and a photosensitive layer coated on a surface of the supporT, the layer comprising the imaging coating formulation according to claim
 3. 